1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same. More specifically, the present invention relates to a semiconductor device of a modular type wherein semiconductor chips such as flip-chips are mounted on a base board adapted for dissipation of the heat caused by the semiconductor chips and a method of manufacturing the same.
2. Description of the Prior Art
FIG. 1 is a sectional view of one example of a conventional semiconductor device of this type. The semiconductor device shown in FIG. 1 comprises a heat sink 1, a hollow flange 2 having a sectional shape as shown, screws 3 for joining the heat sink 1 to the flange 2, a ring gasket 4 for airtight sealing interposed between the heat sink 1 and the flange 2, flip-chips 6 of such as semiconductor integrated chips by way of semiconductor chips, a module base board 7 for mounting the flip-chips 6 thereon by bonding and mounted to the above described flange 2 and having input and output pins 8 connected thereto, and contact metal 5 interposed between the heat sink 1 and the flip-chips 6, whereby a contacting space 9 is formed to be defined by the heat sink 1, the flange 2, and the module base board 7 and to house the flip-chips 6. In assembling such structure, one end of the flange 2 is mounted onto the module base board 7 with the flip-chips 6 mounted thereon. The respective contact metals 5 are placed on the rear surfaces of the respective flip-chips 6, and then the gasket 4 is disposed on the inner side surface of the flange 2. Then with the bottom of the heat sink 1 in contact with the respective contact metals 5, the fixing portion of the heat sink 1 is joined to the other end of the flange 2, whereupon the heat sink 1 and the flange 2 are fixed with the screws 3, thereby to achieve airtight sealing of the flip-chips 6. The heat produced from the respective flip-chips 6 is transferred to the heat sink 1 serving as a heat dissipating member through the contact metals 5 interposed between the rear surfaces of the respective flip-chips 6 and the heat sink 1.
FIG. 2 is a partial sectional view of another example of a conventional semiconductor device of this type. In the example shown in FIG. 2, a leaf spring 10 of a good thermal conductivity is disposed between the flip-chip 6 and the heat sink 1.
With the structure shown in FIG. 1, a major portion of the heat produced by the respective flip-chips 6 is transferred from the rear surfaces of these flip-chips to the contact metals 5 and is further transferred from the contact metals 5 to the heat sink 1, whereupon the heat is dissipated into the air forcedly supplied. Basically the same as that shown in FIG. 1 applies to the structure shown in FIG. 2 and a major portion of the heat produced by the flip-chips 6 is transferred from the rear surfaces of the flip-chips 6 through the leaf springs 10 to the heat sink 1, whereupon the heat is dissipated into the air.
However, with such conventional semiconductor devices, a disadvantage was involved that, in transfer of the heat produced by the respective flip-chips 6 to the heat sink 1 a contact of the rear surfaces of the flip-chips 6 with thermal conducting members between the heat sink 1 and the flip-chips 6, such as the contact metals 6 in FIG. 1 and the leaf springs 10 in FIG. 2, becomes poor, so that a thermal resistance in such portions becomes very large, whereby a sufficient heat dissipating effect can not be attained. The causes of such poor contact include a poor contact due to uneven heights of the flip-chips 6 as shown in FIG. 3A, reduction of the contacting area between the rear surfaces of the flip-chips and the contact metals 5 due to an inclination of the flip-chips 6 as shown in FIG. 3B, and the like, in the case of the structure shown in FIG. 1, and also reduction of the contacting area between the rear surfaces of the flip-chips and the leaf springs 10 due to uneven heights of the flip-chips 6 as shown in FIG. 4, and the like, in the case of the structure shown in FIG. 2.
FIG. 5 is a sectional view of a further example of a conventional semiconductor device of this type. The semiconductor device shown in FIG. 5 comprises a heat sink 15, a cap 16 made of such as ceramics and mounted to the heat sink 15, an adhesive material 17 of a good thermal conductivity, flip-chips 6 of such as semiconductor integrated circuit chips by way of semiconductor chips, a module base board 7 for mounting the flip-chips 6 thereon by bonding and having input and output pins 8 connected to the module base board 7 and mounted to the cap 16 with an adhesive material 18 and adhesive materials 31 interposed between the cap 16 and the flip-chips 6 at the contacting space 9. In assembling the semiconductor device of the above described structure, the adhesive material 31 of a good thermal conductivity and of a solid state, such as a metal of a low melting point of such as indium, solder or the like, is placed on each of the rear surfaces of the respective flip-chips 6 mounted on the module base board 7. Then the adhesive material 18 of a similar material to that of the above described adhesive material 31 is placed on the module base board 7 at the peripheral end thereof and the cap 16 is placed thereon so as to cover the respective flip-chips 6 and so as to be in contact with the above described adhesive materials 31 on the respective flip-chips 6. Then in such a state the assembly is placed in an atmosphere heated to a temperature for melting the above described adhesive materials 31 and 38, whereby the cap 16 is joined to the module base board 7 with the adhesive material 18 to achieve airtight sealing, while the cap 16 is joined to the rear surfaces of the flip-chips 6 with the adhesive material 31. At that time the above described adhesive material 31 is once melted and is then solidified, whereby the joining portion 9 assures the joining of the cap 16 to the flip-chips 6, with the result that a thermal resistance therebetween is decreased. Then the heat sink 15 is joined onto the cap 16 with the adhesive material 17 of a good thermal conductivity.
Since the semiconductor device thus assembled has rear surfaces of the respective flip-chips 6 joined onto the cap 16 with the adhesive material 31, a thermal resistance therebetween is small and the heat produced by the respective flip-chips 6 is effectively dissipated through a heat dissipating member including the above described cap 16 and the heat sink 15.
Another conventional method of assemblage basically comprises substantially the same way of assemblage as in the case shown in FIG. 5; however, as shown in FIG. 6, contact plates 20 of a good thermal conductivity, such as copper, aluminum or the like are interposed between the rear surfaces of the flip-chips 6 and the cap 16 without joining the rear surfaces of the flip-chips 6 and the cap 16 with an adhesive material of a solid state by melting the same, whereby the heat produced by the flip-chips 6 is transferred through the above described contact plates 20 to the cap 16, and as shown in FIG. 7, leaf springs 21 of a good thermal conductivity of such as copper, aluminum or the like are employed to transfer the heat produced by the flip-chips 6 to the cap 16.
However, in the case where the method shown in FIG. 5 is employed, although a preferred thermal conducting effect can be attained since the flip-chips 6 are completely mounted to the cap 16 with the adhesive material 31 and a thermal resistance therebetween is small, an excessive load could be applied to the flip-chips 6 due to a mechanical stress and the like on the occasion of the joining and deterioration of the characteristics, damages and the like are caused. On the other hand, in the case where the methods shown in FIGS. 6 and 7 are employed, although an influence due to the above described stress can be decreased, a contacting area between the thermal conducting member (the contact plates 20 in the case shown in FIG. 6 and the leaf springs 21 in the case shown in FIG. 7) and the flip-chips 6 and the cap 16 becomes small due to diversification of the height of the flip-chips 6, inclinations thereof and the like, as shown in FIGS. 8, 9 and 10, whereby a thermal resistance is increased, with the result that a sufficient heat dissipating effect can not be attained.